This invention relates to a fuel cell system, and more particularly to a replacement gas production and feed system for replacing the reacting gas of a fuel cell with inert gas at the time of start and stop of operation of the fuel cell.
It is well known that a fuel cell is made of a cell stack comprising plural single cells each composed of a pair of fuel electrode and oxidizing agent electrode between which an electrolyte is pinch-held. Fuel containing hydrogen and oxidizing agent such as air or oxygen are fed to the cell stack to generate electricity. Various fuel cells such as an alkaline type, a phosphoric acid type, a fused carbonate type and etc. are classified in accordance with the kinds of their electrolytes or operating temperatures. At the time of start and stop (including emergency stop) of operation of these fuel cells, the gases in fuel and oxidizing agent feed and discharge systems including the bodies of the fuel cells are generally replaced with inert gas such as nitrogen gas in order to secure safety. Especially for the fuel system of each of these fuel cells, the gas replacement is indispensable in controlling the operation of the fuel cell. When the fuel cell whose operation has been stopped is put in operation again, detonating gas is likely to be produced and dangerously explode if the fuel is fed into the fuel system having air or oxygen remaining therein. For that reason, the gas in the fuel system is replaced with the inert gas before the fuel is fed to resume the operation of the fuel cell. When the operation of the fuel cell is stopped, the pressure of the fuel gas is likely to decrease due to the internal discharge of the fuel cell, a temperature change of the like so that air enters into the fuel system to produce detonating gas if the fuel gas is left in the body of the fuel cell. In this case, similar gas replacement with the inert gas is performed to remove the fuel gas from the fuel system to secure safety. If the fuel leaks from the fuel system into the air or oxygen oxidizing agent feed system at the time of start and stop of operation of the fuel cell, detonating gas is likely to be produced and dangerously explode. For that reason, the gas replacement with the inert gas is performed for the oxidizing agent feed system as well as for the fuel system.
In a conventional fuel cell equipment, inert gas which is obtained not from its fuel and oxidizing agent feed systems but is obtained from outside is stored in a storage tank such as a pressure container in order to perform gas replacement as described above. The stored inert gas is fed from the storage tank to the reacting gas system of the fuel cell of the fuel cell equipment at the time of start and stop of operation of the fuel cell. When the stored quantity of the inert gas in the storage tank has decreased to a certain extent, the inert gas needs to be immediately supplemented to remain sufficient in quantity. For that purpose, detailed items of management such as the monitoring of the quantity of the inert gas remaining in the storage tank, the securing of inert gas stockpile and the purchase or acquisition of inert gas are always required to be done. As for a conventional fuel cell equipment used as a portable power source, an inert gas storage tank not only for inert gas in current use but also for inert gas in stockpile needs to be provided and conveyed together with the fuel cell equipment. Therefore, these conventional fuel cell equipments have a problem that it is very difficult to manage the remaining quantity monitoring, purchase or acquisition, storing and supplementing of inert gas.